In fluorescent lamps, ultraviolet (UV) radiation emitted by a mixture of mercury vapor and a noble gas is converted to visible light by a phosphor coating on the inside surface of a lamp envelope. The lamp envelope is sealed and contains mercury vapor at a few millitorr and an inert starting gas such as argon, krypton, neon, helium, or a mixture of these and other gases. A pair of electrodes located within the envelope emits electrons during starting and supplies electrical energy to an arc discharge during operation of the lamp. Electrical leads (inlead wires) coupled through the envelope to each of the electrodes supply electrical energy to the electrodes. A ballast inductor is commonly connected in series with the cathode electrode for limiting the current supplied to the lamp.
Compact fluorescent lamps are configured for mounting in a conventional incandescent lamp socket. Twin tube fluorescent lamps include two substantially parallel tube sections connected at one end. Electrodes are located at the other end of each tube section, and an arc is generated between the electrodes through the full length of each tube section. Double twin tube lamps comprise four substantially parallel tube sections, including two twin tube sections connected through a constriction. A continuous arc is generated between the electrodes through the four tube sections in these lamps.
A ballast inductor and a glow bottle are typically mounted in the base of a compact fluorescent lamp. The glow bottle is connected between the electrodes and acts as a thermal switch to aid in initiating a discharge. When the lamp is cold and is first turned on, current flows through the electrodes and through the glow bottle switch. The electrodes emit electrons which assist in initiating a discharge. After formation of the discharge, the glow bottle switch opens and remains open because there is insufficient voltage across the glow bottle to activate the same.
A recognized drawback of compact fluorescent lamps is the long starting time which may occur at low ambient temperatures. It is not uncommon for twin tube fluorescent lamps, particularly those with long tube sections, to flicker on and off for at least five minutes before sustaining a discharge. In fact, some lamps will continue to flicker and never sustain continuous light emission. It is known that repeated attempts at starting lamps shortens the life of the lamp. In addition, slow starting is unacceptable to users.
There have been many attempts at shortening the starting time of compact fluorescent lamps at low temperatures. Those skilled in the art will recognize that several factors affect the starting of fluorescent lamps. These factors include the following:
1. the arc length of the lamp;
2. the diameter of the lamp envelope;
3. the type of inert gas used and the gas pressure thereof;
4. the quantity of gas impurities;
5. the power supply voltage;
6. the characteristics of the glow bottle; and
7. the temperature of the mercury or ambient temperature.
Despite optimization of most of the above factors, lengthy starting times of compact fluorescent lamps remain a problem at low temperatures.
One approach to decreasing the starting time of compact fluorescent lamps at low temperatures involves using a smaller, higher resistance electrode. The aim is to increase electron emission of the coils of the lamp through the elevated electrode coil temperatures attainable with smaller electrodes. However, this approach has several drawbacks. Because the smaller electrodes have less capacity to carry emissive material coating than larger electrodes, a decrease in lamp life results. Further, the higher operating temperature of the small electrodes creates severe lamp envelope end blackening.
Another approach to increasing the mercury temperature inside compact fluorescent lamps prior to lamp starting involves the use of heater wires or pads which are attached to the lamp envelope. This approach also involves several drawbacks. In particular, the light output is attenuated by the heater wires or pads. In addition, difficulties are involved in manufacturing these lamps. Further, several minutes may still be required to heat the mercury inside the lamp when the lamp is turned on.
Accordingly, a general object of the present invention is to provide an improved compact fluorescent lamp.
Another object of the present invention is to provide a starting aid for compact fluorescent lamps to reduce the starting time of such lamps at low temperatures.